Jim,
The push pier systems work quite well. There are different manufacturers that have their own details, but the principal is the same. They are used all over here in the Tidewater area with great success. They can even be adjusted later on. I spoke with a geotechnical engineer the other day about them. I opined that they are self-testing because they are calibrated for load based on the hydraulic pressure readings they monitor as they push. She said that is fine except if you are over something that may have been fill, you could run into a hunk of old concrete. Another possibility is that you may hit a good stratum, but it turns out to be thin and you eventually punch through to a softer stratum. Also, you don’t want to spread the piles too far apart because your footing results in a grade beam and is usually not reinforced.
A Structural Engineer, P.C.
Glenn C. Otto, P.E.
Virginia Beach, VA
Website: www.astructuralengineeronline.com
-----Original Message-----
From: Jim Wilson [mailto:wilsonengineers@yahoo.com]
Sent: Thursday, April 30, 2009 8:53 AM
To: seaint@seaint.org
Subject: Push piers foundation systems
Is anyone familiar with the Push Pier System provided by Foundation Supportworks, or similar products for that matter? I have settlement under a portion of my garage that needs to be addressed. This is a simple end-bearing pipe pier hydrolically pushed down to bearing.
The system does carry a 25-year warranty and looks to be well designed. I don't know if there are any particular risks or gotchas with installing these systems. They say they usually hit bearing in 20-30 feet but I realize that is a big unknown. There isn't much online to read about these that isn't promotional. I did find one link to a discussion where they warned about the thickness and grade of the steel.
The contractor does not suggest that I hire a geotech to do a study - am I adding a lot of risk by not doing so? It is only a light single-story structure.
They do not suggest the helical pier, either. Soils are sandy gravel. They are not expansive. The upper layer under the foundation may have been fill but I don't know for sure. Settlement is arguably active - notable additional recent movement has been attributed to vibration from paving our driveway last year. Garage is 20 years old and has dropped maybe 2" overall.
Jim Wilson, PE
Stroudsburg, PA